In 2023, pulsar timing arrays announced what could become the first ever discovery of a stochastic gravitational wave background: the random superposition of gravitational waves permeating the cosmos — a vestige of cosmic processes in the Universe. Upcoming datasets are expected to confirm the discovery and provide insight into the origin of this signal.
Key advances
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Pulsar timing arrays worldwide have provided 2σ–4σ evidence for the detection of a gravitational wave signal in the form of a stochastic gravitational wave background consistent with astrophysical expectations.
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By monitoring the deviations in the times of arrival of the radio frequency pulses of a large number of pulsars for many years it is possible to measure the gravitational redshift caused by gravitational waves emitted by far-away sources and travelling through spacetime between the pulsars and the Earth.
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The signal can be explained in terms of the superposition of gravitational waves emitted by supermassive black hole binaries at the centre of galaxies; however, a more speculative origin, rooted in processes taking place in the very early Universe, for example at the quantum chromodynamics energy scale, is not excluded.
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Caprini, C. Strong evidence for the discovery of a gravitational wave background. Nat Rev Phys (2024). https://doi.org/10.1038/s42254-024-00711-6
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DOI: https://doi.org/10.1038/s42254-024-00711-6
